Morphological Filters

Morphological operations were originally designed in the context of set theory. The two basic morphological operators are erosion and dilation. Applied to image processing, an erosion filter tends to reduce the sizes of bright image features by correlation with adjacent dark areas. A dilation filter does just the opposite: it constrains dark features with pixels from surrounding bright areas. Erosion and dilation filters, also known as minimum and maximum filters, respectively, are useful for some noise reduction tasks and also have some interesting applications, mainly specific to deep-sky astrophotography.

A generalization of morphological operations in algorithmic terms leads to a selection filter. The median filter is a particular case of selection filter, with important applications to noise reduction.


Median Filters

Minimum (Erosion) and Maximum (Dilation) Filters